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      1 """Registration facilities for DOM. This module should not be used
      2 directly. Instead, the functions getDOMImplementation and
      3 registerDOMImplementation should be imported from xml.dom."""
      4 
      5 # This is a list of well-known implementations.  Well-known names
      6 # should be published by posting to xml-sig (at] python.org, and are
      7 # subsequently recorded in this file.
      8 
      9 well_known_implementations = {
     10     'minidom':'xml.dom.minidom',
     11     '4DOM': 'xml.dom.DOMImplementation',
     12     }
     13 
     14 # DOM implementations not officially registered should register
     15 # themselves with their
     16 
     17 registered = {}
     18 
     19 def registerDOMImplementation(name, factory):
     20     """registerDOMImplementation(name, factory)
     21 
     22     Register the factory function with the name. The factory function
     23     should return an object which implements the DOMImplementation
     24     interface. The factory function can either return the same object,
     25     or a new one (e.g. if that implementation supports some
     26     customization)."""
     27 
     28     registered[name] = factory
     29 
     30 def _good_enough(dom, features):
     31     "_good_enough(dom, features) -> Return 1 if the dom offers the features"
     32     for f,v in features:
     33         if not dom.hasFeature(f,v):
     34             return 0
     35     return 1
     36 
     37 def getDOMImplementation(name=None, features=()):
     38     """getDOMImplementation(name = None, features = ()) -> DOM implementation.
     39 
     40     Return a suitable DOM implementation. The name is either
     41     well-known, the module name of a DOM implementation, or None. If
     42     it is not None, imports the corresponding module and returns
     43     DOMImplementation object if the import succeeds.
     44 
     45     If name is not given, consider the available implementations to
     46     find one with the required feature set. If no implementation can
     47     be found, raise an ImportError. The features list must be a sequence
     48     of (feature, version) pairs which are passed to hasFeature."""
     49 
     50     import os
     51     creator = None
     52     mod = well_known_implementations.get(name)
     53     if mod:
     54         mod = __import__(mod, {}, {}, ['getDOMImplementation'])
     55         return mod.getDOMImplementation()
     56     elif name:
     57         return registered[name]()
     58     elif "PYTHON_DOM" in os.environ:
     59         return getDOMImplementation(name = os.environ["PYTHON_DOM"])
     60 
     61     # User did not specify a name, try implementations in arbitrary
     62     # order, returning the one that has the required features
     63     if isinstance(features, str):
     64         features = _parse_feature_string(features)
     65     for creator in registered.values():
     66         dom = creator()
     67         if _good_enough(dom, features):
     68             return dom
     69 
     70     for creator in well_known_implementations.keys():
     71         try:
     72             dom = getDOMImplementation(name = creator)
     73         except Exception: # typically ImportError, or AttributeError
     74             continue
     75         if _good_enough(dom, features):
     76             return dom
     77 
     78     raise ImportError("no suitable DOM implementation found")
     79 
     80 def _parse_feature_string(s):
     81     features = []
     82     parts = s.split()
     83     i = 0
     84     length = len(parts)
     85     while i < length:
     86         feature = parts[i]
     87         if feature[0] in "0123456789":
     88             raise ValueError("bad feature name: %r" % (feature,))
     89         i = i + 1
     90         version = None
     91         if i < length:
     92             v = parts[i]
     93             if v[0] in "0123456789":
     94                 i = i + 1
     95                 version = v
     96         features.append((feature, version))
     97     return tuple(features)
     98